1. Field of the Invention
This invention relates to an optical element-mounting substrate and, particularly, to an optical element-mounting substrate in which an optical semiconductor element is optically coupled to an optical fiber or to a lens.
2. Description of the Related Art
A silicon optical bench which is a mounting substrate in which an optical semiconductor element is optically coupled to an optical fiber or to a lens, has been disclosed in Japanese Patent Laid-Open No. 201660/1996. V-Grooves have been formed in the silicon optical bench by anisotropic etching for firmly mounting an optical fiber or a spherical lens thereon.
Further, a silicon optical bench for a small optical module capable of transmitting signals at high speeds has been disclosed in Japanese Patent Laid-Open No. 36182/2001. According to this art, thin-film electrodes are formed on a dielectric film to constitute draw-out wirings for the optical semiconductor element. Further, bonding pads of the thin-film electrodes have been formed on a region of the silicon substrate from where the dielectric film has been removed.
Japanese Patent Laid-Open No. 315707/1993 discloses a structure equipped with a thin-film temperature sensor formed of a V50Ru50 alloy.
It was, however, found that the above related arts are not enough for providing an optical element-mounting substrate that makes it easy to optically couple the optical semiconductor element to the optical fiber or to the lens and that can be highly integrated while suppressing deterioration in the high-frequency signals. Japanese Patent Laid-Open No. 201660/1996 fails to describe members for feeding an electric current to the optical semiconductor element which is necessary for really driving the optical semiconductor element on a rugged substrate having V-grooves formed by anisotropically etching silicon.
On the other hand, an increase in the speed of data transmission is accompanied by a deterioration of signals transmitted through the thin-film electrodes and bonding wires. To suppress the deterioration, it is important to match the impedance between the optical semiconductor element and the thin-film electrode, and to suppress the parasitic inductance component by decreasing the length of the bonding wires as much as possible. To match the impedance, it is necessary to highly precisely form thin-film electrodes to form a wiring pattern on a rugged substrate in which V-grooves are formed. In order to shorten the length of the bonding wires, further, the arrangement of the thin-film electrodes must be contrived. Upon handling high-frequency signals, further, noise such as overshooting occurs in the pulse signal components. Therefore, a filter circuit (RC circuit or the like circuit) must be used for cutting noise.
According to Japanese Patent Laid-Open No. 36182/2001, the structure becomes complex since members are formed on other substrates for feeding an electric current to the optical semiconductor element that is necessary for really driving the optical semiconductor element, and many substrates are coupled together through wires. Besides, there is no groove for mounting the optical fiber or the lens, and the thin-film electrodes are formed on the silicon substrate without ruggedness. Therefore, a separate component is necessary, such as an optical ferrule for mounting an optical fiber and a lens in addition to the silicon optical bench. This results in an increase in the number of parts of the optical module, and an increased period of time is needed by the assembling steps for optically coupling the optical components together, causing the productivity to decrease. Further, coupling losses among the components tend to build up.